Film advance braking system

ABSTRACT

In a camera provided with an electric motor for advancing film; switching means for sequentially connecting the motor first with a source of potential to advance the film, and then with a shunt to dynamically brake the film-advancing mechanism in response to detection of a code indicia on the film. The switching means can comprise a two-way switch with a common terminal actuatable from one switching position to the other by a sensor that detects perforations in the film. According to an alternative embodiment, the switch means comprises three sliding contacts adapted to engage a conductive strip on the film to electrically connect one of the terminals alternately with the other two terminals.

United States Patent [72] Inventor Donald M. Harvey 1,950,518 3/ 1934 Read 352/92 Rochester, N.Y. 2,948.,203 8/1960 Hadley et al. 352/92 [21 App]. No. 754,794 3,069,570 12/1962 Abadie 200/ 6 l 1 3X [22] Filed Aug. 23, 1968 3,148,585 9/1964 Armstrong et al. 226/45 [45] Patented Mar. 9, 1971 3,148,605 9/1964 Peterson et al. 226/33X [73] Assignee Eastman Kodak Company 3,169,460 2/ 1965 Winkler et a1. 95/31 Rochester, N.Y. 3,301,628 l/ 1967 Hellmund 352/92X 3,470,803 10/1969 Fukuoka et a1. 95/31 [54] FILM ADVANCE BRAKING SYSTEM 8 Claims, 7 Drawing Figs.

[52] US. Cl 95/3], 226/33, 226/45, 242/57, 352/92, 352/236 [51] Int. Cl G031) l/l4, G03b 19/04, B65h 25/00 [50] Field of Search 95/31;

Primary Examiner-Samuel S. Matthews Assistant Examiner-Joseph F. Peters, .lr. Attorneys-R. W. Hampton and Daniel E. Sragow ABSTRACT: In a camera provided with an electric motor for advancing film; switching means for sequentially connecting the motor first with a source of potential to advance the film, and then with a shunt to dynamically brake the film-advancing mechanism in response to detection of a code indicia on the film. The switching means can comprise a two-way switch with a common. terminal actuatable from one switching position to the other by a sensor that detects perforations in the film. According to an alternative embodiment, the switch means comprises three sliding contacts adapted to engage a conductive strip on the film to electrically connect one of the terminals alternately with the other two terminals.

Patented March 9, 1971 2 Sheets-Sheet 1 FIG.

DONALD M. HARVEY i Z i ATTORNEYS Patented March 9, 1971 2 Sheets-Sheet 8 S m N m w A FILM ADVANCE BRAKING SYSTEM BACKGROUND OF THE INVENTION In still cameras which are provided with an electric motor for advancing the film after each exposure, it is conventional to provide a cam or similar structure to control the activation of the motor which drives the film-advancing mechanism and to cock the shutter so that the next exposure may be made. This structure has the disadvantage of controlling the transport of the film by a fixed number of revolutions of the cam and thus does not transport a uniform quantity of film as more and more film is wound onto the takeup spool. The location of the exposed portions thus is not uniform, thereby causing difficulties in the rapid processing of the film when using equipment which automatically frames the exposures.

Attempts to insure that a constant length of film is transported in each cycle of the film-advancing mechanism have resulted in structures which control the activationof the filmadvancing mechanism by mechanically measuring the quantity of film transported. These structures have two inherent disadvantages. The first is the relative complexity of the structures, which must be made very precise and are thus more subject to mechanical failure. The second is their dependence upon measurement of the amount of film which has been transported. An inaccurate measurement due to a tear in the sprocket holes or some other mechanical failure will result in SUMMARY OF THE INVENTION An object of this invention is to provide a simple and accurate control for the film-advancing mechanism which insures that a uniform length of film will be transported during each cycle of the mechanism.

A further object of the invention is to provide a construction which will electrically short the motor after a uniform quantity of film has been transported thereby dynamically braking the film-advancing mechanism.

Briefly, the invention comprises, in a camera having an electric motor-driven film-advancing mechanism, an electric circuit which contains the motor, a battery and switching means for either powering the motor by means of the battery or braking the motor by means of shorting it. Means activated by the termination of the exposure shutter close the motor-battery circuit and maintain it closed while shutter recocking action takes place. The motor-battery circuit is thereafter maintained closed until an amount of film has been transported which is equivalent to one frame. The motor-battery circuit is then opened and the motor leads shorted. Electrical shorting of the moor leads rapidly and accurately stops the film advance mechanism.

Shorting of the motor is accomplished by means on the film itself. In one embodiment a pawl engages a sprocket hole; in another embodiment a brush contacts a conductive stripe on the film backing.

BRIEF DESCRIPTION OF THE DRAWINGS The subject matter which is regarded as my invention is particularly pointed out and claimed in the concluding portion of this specification. The invention, however, as to its organization and operation, together with further objects and advantages thereof, will best be understood by reference to the following description taken in connection with the accompanying drawing in which:

P16. 1 is a schematic diagram of such a braking system;

FIG. 2-4 are fragmentary views showing three sequential positions of the cam and pawl;

FIG. 5 is a schematic view of an alternate embodiment of the braking system; and

FIGS. 6-7 are fragmentary views showing sequential positions of the contacts.

Referring to FIG. 1, a camera housing (not shown) contains a film supply spool 11 and a film takeup spool 2. The film 12 passes from the supply spool l l to the takeup spool 2 and contains regularly spaced perforations 4, which are spaced a distance of one frame along the direction of film advance. An electric motor 1, preferably a low-impedance permanent magnet motor, is coupled by conventional means (not shown) to the takeup spool 2.

Fixedly mounted in but electrically insulated from the camera housing, if such housing is conductive, are spring arms 13 and 14, which have electrical contacts 6 and 9 at their free ends respectively. Also fixedly mounted in the camera housing is a spring arm 5 with a pawl 3 which is integral therewith. A battery 10 or other source of potential has one terminal connected to spring arm 14 and thereby to contact 9. The other terminal of the battery 10 is connected to one terminal of the motor 1- and also to spring arm 13 and thereby to contact 6. The other terminal of the motor is connected to spring arm 5 which is normally biased into contact with contact 6-when pawl 3 extends through one of the perforations 4 in the film 12. Cam or lever 7 is mounted on pin 8 which is interconnected with the shutter mechanism (not shown) so that cam 7 is rotated in a counterclockwise direction upon activation of the shutter mechanism.

FIG. 1 shows the film advance mechanism just prior to completion of the shutter exposure. Pawl 3 extends through a perforation 4 in the film l2 and arm 5 is biased into contact with contact 6 so that the motor leads are electrically shorted through spring arm 5, contact 6, and spring arm 13. When the shutter exposure has been completed, cam 7 is rotated in a counterclockwise direction about pin 8 and engages spring arm 5, as in FIG. 2, forcing arm 5 off contact 6 and into engagement with contact 9. Battery 10 is then in series with motor 1 which begins to drive the takeup spool 2 to advance the film. It can be seen that movement of arm 5 from contact 6 to contact 9, causes pawl 3 to be removed from perforation 4 in the film. The film is then free to pass under pawl 3 onto the takeup spool.

The shutter mechanism rotates cam 7 in a clockwise direction as in FIG. 3. As cam 7 is rotated, the spring bias of arm 5 causes it to remain in contact with the cam, until pawl 3 comes to rest upon the upper surface of film 12. Further rotation of cam 7 as in FIG. 4 disengages cam 7 from contact with arm 5 which is held stationary by means of pawl 3 resting upon the upper surface of film 12. In this position, arm 5 is still in contact with contact 9 and the battery-motor circuit is still closed.

The motor 1 continues to drive the takeup spool 2, until the next perforation 4 in film 12 passes under pawl 3. The perforation is positioned at a distance of exactly one frame from the previous perforation, in accordance with U. S. Pat. No. 3,260,182, issued Jul. 12,1966, to Nerwin. Pawl 3 drops into the perforation as in FIG. 1 and spring arm 5 returns to its normal bias position. The motor-battery circuit is thus disconnected. Arm 5 is thus biased against contact 6, thereby shorting the terminals of the motor. The motor, since it now acts as a generator with a very large load, is dynamically braked and rapidly stops rotating. The film takeup spool 2, which is driven by the motor, will also stop, and exactly one frame of film will have been advanced from film supply spool 11 to film takeup spool 2.

While the film advance braking system described above advances exactly the same quantity of film in each cycle, it may transport more or less film should the perforation not be cleanly cut in the film or should a tear occur in the film. The embodiment shown in FIGS. 5-7 illustrates a braking system which is not dependent upon the presence or position of a hole in the film.

Referring to FIG. 5, a camera housing (not shown) contains a film supply spool 11' and a film takeup spool 2', with film l2 passing from supply spool IT to the takeup spool 2'. An electrically conductive coating 16, such as silver, is applied to the back of film 12' in a substantially straight strip with uniform width. At intervals of exactly one frame, the film backing is masked in such a way as to allow deposition of a rectangular area of conductive coating 17, continuously connected with the main coating strip 16 and extending outwardly from the main strip 16 towards the edge 22 of the film 12. Simultaneously, a rectangular area 15, which is normally coated with conductive material is masked so as to remain uncoated. This rectangular area 15 is located directly across the conductive strip 16 from rectangular area 17, but is slightly longer in the direction of film travel than rectangular area 17 and does not extend the full width of the main strip 16.

An electric motor 1, preferably a low-impedance permsnent magnet motor, is coupled by conventional means (not shown) to the takeup spool 2'. Fixedly mounted are spring arms 13' and 14' which have electrical contacts 6' and 9' integral therewith. Also fixedly mounted in the camera housing is spring arm Fixedly attached in a transverse direction to am 5' and at the free end thereof is member 20. Fixedly attached to member 20 at end 23 is contact 21 which is normally disposed directly above and a short distance from spring arm 14'. Fixedly attached to the other end 24 of member 20 is contact 3'.Contacts 3', 6, and 9' are normally biased so as to rest upon film 12' by action of spring arms 5', 13', and 14'. Contact 3' rests in that portion of main coating strip 16 which lies closest to edge 22 of film stripgl2'. Contact 9 lies further away from edge 22 than contact 3', at such a distance as to 16 but so as to never rest upon main coating strip 16.

A battery or other source of potential has one terminal connected to spring arm 14' and thereby to contact 9'. The

other terminal of the battery 10 is connected to one terminal of the motor land also to spring'arm l3 and thereby to contact 6. The other terminal of motor l is connected to spring arm 5 and thereby to contacts 3' and 21. Rod 18 is interconnected with the shutter mechanism (not shown) and rotatable thereby. Cam 7 is of an electrically nonconductive material and is mounted on rod 18 so as to rotate in a counterclockwise direction upon completion of the shutter exposure.

FIG. 5 shows this embodiment of the film advance mechanism just prior to activation of the shutter mechanism. Contact 9 is resting upon the film in uncoated area 15. Contact 6 is resting upon the film in coated area 17 and is connected with contact 3' which rests in the main coating strip 16. The motor leads are electrically shorted through spring arm 5, contacts 3' and 6' and spring arm 13. When the shutter mechanism has completed the exposure, cam 7 is rotated in a counterclockwise direction by rod 18, as in FIG. 6, and engages spring arms 13' and 14'. As arms 13' and 14' are forced upwards, contacts 6' and 9' are raised off the film 12 and arm 14'is brought into contact with contact 21. Battery 10 is then in series with motor 1, which begins to drive the takeup spool 2 so as to advance the strip of film.

The shutter mechanism cocks cam 7 as in FIG. 7 by rotating rod 18 and thereby causing cam 7 to rotate in a clockwise direction. As cam 7 rotates, the spring bias of arms 13' and 14 causes them to remain in contact with cam 7 until contacts 6' and 9 come into contact with the film strip. As the film has been advanced, contact 6 will now rest upon the uncoated film 12'. Contact 9' will rest upon the coated strip 16 and the motor-battery circuit is still closed.

Motor 1 will continue to drive takeup spool 2', until the next areas and 17 pass under contacts 9' and 6' respectively. These areas are at a distance of one frame from the corresponding area which were under contacts 9' and 6' at the beginning of the cycle. As contact 9 now will rest in an uncoated area 15, the motor-battery circuit will be disconnected. Contact 6' will rest in a coated area 17 and the motor leads will be electrically shorted through arm .13, contacts 3' and 6' and arm 5. Motor 1 is dynamically braked and rapidly stops rotating. Film takeup spool 2', which is driven by motor 1, will also stop, and exactly one frame of film will have been advanced from film supply spool 1 l' to film takeup spool 2.

Although the foregoing description relates to specific embodiments of the invention, it will be understood that variations and modifications thereof can be effected within the spirit and scope ofthe invention as described hereinabove and as defined by the following claims.

I claim:

1. In a photographic camera adapted to receive a strip of film which has a conductive stripe on one surface, said conductive stripe having irregularities at regular intervals, an electrically driven film-advancing mechanism comprising:

a. an electric motor;

b. a source of electric potential for energizing said motor;

c. film takeup means;

d. means interconnecting said motor and said takeup means for operating the latter in response to operation of the former;

e. first switch means for interconnecting said motor and said potential source;

' f. second switch means for shorting said motor;

g. means cooperating with said first and second switch means for sequentially operating said first and second switch means to drive the motor thereby advancing said film and subsequently shorting the motor; and

h. said second switch means being adapted to cooperate with an irregularity of said stripe in order to brake said motor and takeup means after a predetermined length of film has been advanced.

2. In a photographic camera adapted to receive a strip of film which has a conductive stripe on one surface, said conductive stripe having irregularities at regular intervals, an electrically driven film-advancing mechanism comprising:

a. an electric motor;

b. film takeup means;

c. means interconnecting said motor and said takeup means for operating the latter in response to operation of the former;

d. means for sensing the irregularity of the stripe; and

e. means for sequentially operating said motor, and for then braking said takeup means when a stripe is sensed.

3. In a photographic camera adapted to receive film having code indicia, and having a film advance mechanism driven by an electric motor having a pair of terminals through which it is adapted to be energized by a source of electric potential, means for controlling the electrically driven film-advancing mechanism comprising:

a. a pair of input terminals adapted for connection to such a source of electric potential;

b. actuatable switch means for alternatively connecting said motor terminals with said input terminals for energizing the motor to advance film in the camera or with a shunt to brake said film advance mechanism;

c. means for actuating said switch means to advance the film;

d. means for sensing the code indicia on the film; and

e. means associated with said sensing means for actuating said switch means in response to detection of a code indicia on the film to brake the motor after the film has been advanced to a position predetermined by the sensed code indicia.

4. In a photographic camera adapted to receive perforated film, and having a film advance mechanism driven by an electric motor having a pair of terminals through which it is adapted to be energized by a source of electric potential, means for controlling the electrically driven film advance mechanism comprising:

a. a pair of input terminals adapted for connection to such a source of electric potential;

b. switch means including a movable contact connected to one of the motor terminals, said movable contact being movable to a first switch position to connect said motor terminals with said input terminals to energize the motor and thereby advance film in the camera, and to' a second switch position to shunt said motor terminals to brake said film advance mechanism; I

means for biasing said movable contact to its second switch position in which the motor terminals are shunted;

d. means associated with said movable contact for selectively moving it against the force of said bias means to its first switch position for advancing the film; and

e. sensing means for detecting film perforations, said sensing means being associated with said movable contact for maintaining said contact in its first switch position until it detects the presence of a perforationin the film and for permitting said contact to move to its second switch position when said sensing means detects the presence of a perforation in the film.

5. In a photographic camera adapted to receive a-strip of film having on one surface a conductive strip that has discontinuities at regular intervals, and 'having a film-advancing mechanism driven by an electric motor having a pair of terminals through which it is adapted to be energized by a source of electric potential, means for controlling the electrically driven film advancingmechanism, comprising:

a. a pair of input terminals adapted for connection to such a source of electrical potential;

b. first switch means actuatable to connect said motor terminals with said input terminals for energizing the motor to advance film in the camera;

c. second switch means actuatable to' shunt the motor terminals to brake the motor; and

gize the motor to advance the film and then to shunt the motor terminals in order to brake the motor and the filmadvancing mechanism after a predetermined length of film has been advanced. -6. For use in a photographic camera having first, second and third electrical contacts disposed to engage a film'advanced through the camera, a'photographic strip of film comprising:

a. abase layer; and

b. a conductive strip on said base layer having a continuous central strip portion continuously engageable by the first contact as the film is advanced through the camera, and

. having a noncontinuous strip portion on each side of and contiguous with the central strip'portion, each noncontinuous strip portion being adapted for intermittent engag'ement with the second and third contacts, respectively, as the film is advanced through the camera, whereby the first contact is selectively electrically connected with the second and third contacts as the film is advanced through the camera.

7. Means for controlling an electrically driven film advance mechanism in a photographic camera adapted to receive film,

having one surface a conductive strip, theconductive strip including a continuous central strip portion' adaptedfor continumeans including said conductive strip for sequentially operating said first and second switch means first to enerous engagement by a first contact as the film is advanced through the camera and a noncontinuous strip portion on each side of and contiguous with the central strip portion, each noncontinuous strip portion being adapted for intennittent engagement with second and third contacts, respectively, for selectively electrically connecting-the second and third contacts with the first contact as the film is advanced through the camera, the camera having afilm-advancing mechanism driven by an electric motor having apair of terminals through which it is adapted to be energized by a source of electric potential, said control means comprising: a

a. a pair of input terminals adapted for connection to such a source of electric potential;

b. first switch means including first and second contacts adapted to engage the central portion and one of the side portions of the conductive strip on such a film in the camera, said first contact being connected to one of the motor terminals and said second contact being connected to one of the input terminals, the other input terminal being connected to the other motor terminal so that electrical connection between said first and second contacts connects the motor terminals with the input terminals to energize the motor and advance film in the camera;

. c. second switch means including said first contact and a third contact connected. to the other motor terminal and adapted to engage the other side portion of the conductive strip, such that electrical connection between said first and third contacts shunts the motor terminals to brake the film-advancing mechanism;

a d. means for selectively engaging said contacts with the conductive strip; and

e. means for electrically connecting said first and third contacts independently of the conductive strip on the film.

8. Means for controlling an electrically driven film-advancing mechanism in a photographic camera adapted to receive film having on one surface a conductive strip, the conductive strip including a continuous central strip portion adapted for continuous engagement by a central contact as the film is advanced through the camera, and a noncontinuous strip portion on each side of and contiguous with the central strip portion, each non-continuous strip portion being adapted for intermittent engagement with an outer contact as the film is advanced through the camera for selective electrical connection with the central contact, the camera having a film advancing mechanism driven by an electric motor having a pair of terminals, said control means comprising: I

a. contact means for engaging independently the central and outer portions of such a conductive strip on a film in the camera;

b. means connected with said contact means for shunting the motor terminals through the conductive strip at predetermined positions on the-film; and

c. means for energizing said electric motor through the conductive strip for advancing said film between said predetermined positions on the film. 

1. In a photographic camera adapted to receive a strip of film which has a conductive stripe on one surface, said conductive stripe having irregularities at regular intervals, an electrically driven film-advancing mechanism comprising: a. an electric motor; b. a source of electric potential for energizing said motor; c. film takeup means; d. means interconnecting said motor and said takeup means for operating the latter in response to operation of the former; e. first switch means for interconnecting said motor and said potential source; f. second switch means for shorting said motor; g. means cooperating with said first and second switch means for sequentially operating said first and second switch means to drive the motor thereby advancing said film and subsequently shorting the motor; and h. said second switch means being adapted to cooperate with an irregularity of said stripe in order to brake said motor and takeup means after a predetermined length of film has been advanced.
 2. In a photographic camera adapted to receive a strip of film which has a conductive stripe on one surface, said conductive stripe having irregularities at regular intervals, an electrically driven film-advancing mechanism comprising: a. an electric mOtor; b. film takeup means; c. means interconnecting said motor and said takeup means for operating the latter in response to operation of the former; d. means for sensing the irregularity of the stripe; and e. means for sequentially operating said motor, and for then braking said takeup means when a stripe is sensed.
 3. In a photographic camera adapted to receive film having code indicia, and having a film advance mechanism driven by an electric motor having a pair of terminals through which it is adapted to be energized by a source of electric potential, means for controlling the electrically driven film-advancing mechanism comprising: a. a pair of input terminals adapted for connection to such a source of electric potential; b. actuatable switch means for alternatively connecting said motor terminals with said input terminals for energizing the motor to advance film in the camera or with a shunt to brake said film advance mechanism; c. means for actuating said switch means to advance the film; d. means for sensing the code indicia on the film; and e. means associated with said sensing means for actuating said switch means in response to detection of a code indicia on the film to brake the motor after the film has been advanced to a position predetermined by the sensed code indicia.
 4. In a photographic camera adapted to receive perforated film, and having a film advance mechanism driven by an electric motor having a pair of terminals through which it is adapted to be energized by a source of electric potential, means for controlling the electrically driven film advance mechanism comprising: a. a pair of input terminals adapted for connection to such a source of electric potential; b. switch means including a movable contact connected to one of the motor terminals, said movable contact being movable to a first switch position to connect said motor terminals with said input terminals to energize the motor and thereby advance film in the camera, and to a second switch position to shunt said motor terminals to brake said film advance mechanism; c. means for biasing said movable contact to its second switch position in which the motor terminals are shunted; d. means associated with said movable contact for selectively moving it against the force of said bias means to its first switch position for advancing the film; and e. sensing means for detecting film perforations, said sensing means being associated with said movable contact for maintaining said contact in its first switch position until it detects the presence of a perforation in the film and for permitting said contact to move to its second switch position when said sensing means detects the presence of a perforation in the film.
 5. In a photographic camera adapted to receive a strip of film having on one surface a conductive strip that has discontinuities at regular intervals, and having a film-advancing mechanism driven by an electric motor having a pair of terminals through which it is adapted to be energized by a source of electric potential, means for controlling the electrically driven film advancing mechanism, comprising: a. a pair of input terminals adapted for connection to such a source of electrical potential; b. first switch means actuatable to connect said motor terminals with said input terminals for energizing the motor to advance film in the camera; c. second switch means actuatable to shunt the motor terminals to brake the motor; and d. means including said conductive strip for sequentially operating said first and second switch means first to energize the motor to advance the film and then to shunt the motor terminals in order to brake the motor and the film-advancing mechanism after a predetermined length of film has been advanced.
 6. For use in a photographic camera having first, second and third electrical contacts disposed to engage a film advanced through the camera, a photographic strip of film cOmprising: a. a base layer; and b. a conductive strip on said base layer having a continuous central strip portion continuously engageable by the first contact as the film is advanced through the camera, and having a noncontinuous strip portion on each side of and contiguous with the central strip portion, each noncontinuous strip portion being adapted for intermittent engagement with the second and third contacts, respectively, as the film is advanced through the camera, whereby the first contact is selectively electrically connected with the second and third contacts as the film is advanced through the camera.
 7. Means for controlling an electrically driven film advance mechanism in a photographic camera adapted to receive film having one surface a conductive strip, the conductive strip including a continuous central strip portion adapted for continuous engagement by a first contact as the film is advanced through the camera and a noncontinuous strip portion on each side of and contiguous with the central strip portion, each noncontinuous strip portion being adapted for intermittent engagement with second and third contacts, respectively, for selectively electrically connecting the second and third contacts with the first contact as the film is advanced through the camera, the camera having a film-advancing mechanism driven by an electric motor having a pair of terminals through which it is adapted to be energized by a source of electric potential, said control means comprising: a. a pair of input terminals adapted for connection to such a source of electric potential; b. first switch means including first and second contacts adapted to engage the central portion and one of the side portions of the conductive strip on such a film in the camera, said first contact being connected to one of the motor terminals and said second contact being connected to one of the input terminals, the other input terminal being connected to the other motor terminal so that electrical connection between said first and second contacts connects the motor terminals with the input terminals to energize the motor and advance film in the camera; c. second switch means including said first contact and a third contact connected to the other motor terminal and adapted to engage the other side portion of the conductive strip, such that electrical connection between said first and third contacts shunts the motor terminals to brake the film-advancing mechanism; d. means for selectively engaging said contacts with the conductive strip; and e. means for electrically connecting said first and third contacts independently of the conductive strip on the film.
 8. Means for controlling an electrically driven film-advancing mechanism in a photographic camera adapted to receive film having on one surface a conductive strip, the conductive strip including a continuous central strip portion adapted for continuous engagement by a central contact as the film is advanced through the camera, and a noncontinuous strip portion on each side of and contiguous with the central strip portion, each non-continuous strip portion being adapted for intermittent engagement with an outer contact as the film is advanced through the camera for selective electrical connection with the central contact, the camera having a film advancing mechanism driven by an electric motor having a pair of terminals, said control means comprising: a. contact means for engaging independently the central and outer portions of such a conductive strip on a film in the camera; b. means connected with said contact means for shunting the motor terminals through the conductive strip at predetermined positions on the film; and c. means for energizing said electric motor through the conductive strip for advancing said film between said predetermined positions on the film. 